More than 200,000 people living in care homes across England are at risk of being given the wrong medication due to lax behaviour among the staff, government inspectors warned last night.

The Commission for Social Care Inspection said 8,000 nursing and care homes failed to meet national minimum standards for handling drugs prescribed for residents. The commission said: "Around 210,000 people live in these 8,000 homes. Some are extremely old, others very young. Some have severe physical or learning disabilities or other serious long-term illnesses. The medication they receive can make a huge difference to their quality of life."

The commission gave the example of a care home resident who was prescribed antibiotics on a Thursday evening, but did not get them until the following Tuesday afternoon. As a result, the resident had to be admitted to hospital.

At another home with poor record-keeping, a resident was given a dose of insulin twice one morning. At a third home pots of pre-prepared medication were given to the wrong residents.

One care worker in north-west England persistently gave 10 times the prescribed dose of a liquid medicine over several weeks to a resident with learning difficulties. When the mistake was discovered, the care worker was moved, but not retrained.

The commission found little evidence of improvement in medication control in spite of a £48m programme to improve the qualifications of care workers over the past three years. "The primary responsibility for this failure rests with the homes themselves," it said.

Dame Denise Platt, chair of the CSCI, said: "It is vital that all care homes treat this issue with the utmost seriousness."

The care services minister Liam Byrne told the Guardian that the report was important evidence of the problems within the sector. Today he will announce a new registration, training and vetting system for the 750,000 people working with vulnerable children and adults. "This is a sector with too many untrained workers," he said. "Registration will provide the confidence that people who use the services deserve."

The General Social Care Council, which already runs a registration system for social workers, will extend the list to all care workers in residential homes and domiciliary carers. The council will consult on levels of training required for registration, how to fund the new system, and how best to vet care workers.

Mr Byrne said that the plan was in place before it emerged last month that ministers in the Department for Education and Skills had given the go-ahead for registered sex offenders to work with children. The row led to an emergency review.

Mr Byrne, who will address the Skills for Care conference today, will also announce a £600,000 joint research project with Comic Relief to look at the problem of elder abuse.